1. Field of the Invention
The present invention relates to a method for eliminating noise from an image generated by an image sensor, and more particularly, to a method for eliminating noise from an image generated by an image sensor that can remarkably enhance the picture quality of the image by segmenting a feature of the image generated by the image sensor and adaptively eliminating the noise from the image in consideration of the directionality of a contour existing in the image.
2. Description of the Related Art
In general, an image sensor is a device, which converts light detected by each of light detecting units (e.g., photodiodes) arranged in a two-dimensional matrix configuration into an electrical signal to generate an image. An electrical signal value detected by a light detecting unit and quantificated becomes a unit pixel constituting an image. Thus, each pixel of an image detected by an image sensor includes a considerable noise due to internal and external factors, such as the product quality of the image sensor or peripheral light quantity in an light detecting environment, which is a main factor deteriorating the picture quality of the image. Therefore, to improve the picture quality of the image generated by the image sensor, it is necessary to properly correct signal values generated by pixels including a noise.
To decrease a noise in an image generated by an image sensor, a variety of processing techniques have been proposed. Of such processing techniques, the simplest one is a method in which a low pass filter (LPF) is applied to the image. LPF may adjust a noise elimination level by taking a simple average value of a central pixel from which it is necessary to eliminate a noise, and peripheral pixels around the central pixel, or by using a technique obtaining a weighted average. Such a method employing the LPE has a small computational amount and shows a relatively good performance in noise elimination in a flat area of an image. However, if the LPE is applied to all the pixels constituting an image, contour information is decreased together with noise component of the image, thereby lowering the definition of the image and deteriorating the picture quality of the image.
To address the aforementioned problem, a related art noise eliminating method has been proposed, in which LPF is selectively applied only to a pixel including a noise component using a relationship between a central pixel and peripheral pixels. However, the related art method has a limitation in correctly discriminating noise and contour information. Also, since the application of LPF using all of the central pixel does not consider the direction of the contour, a problem that the contour of the image is blurred still exists.
A contour-preserving noise filtering method is the most widely used at the present time. To complement the problems in the aforementioned two methods, this method extracts directionality information of a contour using relationship between a central pixel and peripheral pixels and applies one-dimensional LPF in the direction of the contour to preserve the definition of an image and at the same time eliminate a noise. Also, this method is useful for design of hardware since it has a proper computational amount and complexity. However, the related art contour-preserving noise eliminating method effectively decreases a noise in a specific image region in which a contour exists but has a limitation in eliminating the noise in a flat region. Also, since the related art contour-preserving noise eliminating method does not consider the complexity of an input image, the illuminance of a pixel, a pattern of a noise or the like, it has a problem in that the noise is not effectively decreased.